Molding sand and method of controlling flowability of same



Patented Aug. 7, 1945 TIDILING FLOWABIIJ'I'Y 01'' 1mm in Wood,Cleveland, on, ma Alu- America,

minum Company of corpora tion of Pennsylvania u h. Pa a No Drawing.Application November :1, 1941,

' sel'lll No. new:

s Claims. (oi. 22-10:)

I This invention relates to the art of casting metal members in sandmolds, and is more particularLv concerned with the provision of a methodor controlling, increasing, and maintaining the flowability of usedgreen sands.

. In present sand foundry practice, green sands areemployed for thecasting ct a variety of metals, including the light metals aluminum,magnesium, and their alloys. The constituents of such sands varysomewhat, depending on the use to which they are put, but most of themcontains clay bonding material. Sands used for ma'singmolds in whichmagnesium is cast are usually bonded with bentonite and contain certainadditional substances toinhibit oxidation of the molten metal. Forexample, relatively small amounts of various inhibiting agents such asboric acid and sulfur are introduced into the sand. Such substances asglycerine, ethylene I glycol, diethylene glycol, or otherpo yhydricalcohols which are disclosed in U..S.' Patent No. Q 1,888,453 arefrequently employed, usually in combination with the boric acid andsulfur. The" use of small amounts of certain fluorides that 25 ofsubstances which control the flowability and will decompose or vaporizehas been proposed asanother-means of inhibiting oxidation of moltenmagnesium in sand molds.

Itis important-that molding sand possess ir- 1 'so its shape duringhandling and operations.

taln desired p ysical characteristics. It should be relatively strong sothat the mold will retain However, while the sand should have-therequisite strength, it should not possess this property in such highdegree as to be regarded as tough The sand should also be relativelyflowable, that is',-take the shape of the pattern easily when the moldisbeing made. This property of flowability Y permits the sand, whenrammed, to conform to every portion or the pattern, and thus enables theproduction of castings having sharply deflned contours and smoothsurfaces.

In ordinary foundry practice, the molding sand is used over and overagain, and it is de-' sirable that the sand retain its initial P11181011properties throughout the period of use. Ithas been found; however. thatwith continued usage sands bentonite'or other-similar bonding materialshave a tendency to become somewhat toughersnd less flowable. .Buchbonding materials are herein referred to as argillaceous bondingsubstances; This tendency seems tobe '4 cent sulfur, Ito-2 percent'boric acid, with orwinioui about 1.5 to 2.5 per cent by weightorglycol or other suitable inhibiting agent.

makes is ramming of the molds much more diflicult. It is not fullyunderstood why this decrease in flowability should occur, but it is"thought to relate, to-the polymerization and colloidal suspension orvarious constituents in the It is, therefore, an object of thisinvention to overcome the foregoing deficiency of used molding sands.More particularly, it is an object toprovide a means of restoring theinitial flowability of a used molding sand and to control the samethroughout the subsequent period of use of the sand. Astiil furtherobject-is to attain such results inmolding sands used in the casting oflight metals, particularly magnesium.

I have discovered that potassium fluoride, or sodium fluoride, or both,when introduced into tough sand in suitable amount, reduce the toughnessand increase the flowability. 'I'hroughuse of these compounds, it ispossible not only to attain these results but also to control themthroughout the subuquent period of use of the sand. I'brthepurpose of myinvention, these fluorides are considered as constituting a grouptoughness of molding sands containing bentonite or similar argillaceousbonding material. While 1 either of the fluorides, or mixtures of them,may be employed, I prefer to use potassium fluoride since this material'seems to give somewhat superior results. In general, the type ofmolding sands to which I propose to add sodium or potassium fluoridemay'be either natural or synthetic. Synthetic ll sands generally containa mixture of about 90 to! percentsharpsillcasand andaboutflt'o 5 percent bentonite or other similar bonding mawhereas. natural molding sandsusually contain an even larger per cent of a bonding medium. To either ye of sand I add about 0.10 to 2.0 per cent of either sodium fluoride orpotassium fluoride, and where a mixture is employed, the total amountshould not exceed about iper cent nor should the minimum amount or eachfluoride be less than 0.1 per cent, though,

as stated above. I prefer to employ only potassium fluoride. when thislatter substance is employed;

it is iserably added within the limits of 0.25

to 0.5 per cent. These flgures represent "by weight of his in additionto .the above named substances, a suitablemagnesiumnioldingeandwillalsocontainltoiiper The sodiumand potassiumfluoride addition has very little, it any, oxidation inhibiting eflectin magnesium molding sands, and therefore cannot be considered asbelonging to the group of oxidation inhibitors used in such sands.

It has been noted that with the continued usage of the sand to whichsodium or potassium fluoride has been added, some small loss oi theadded fluoride may occur. In such instances it is very important thatthe fluoride content of the sand be maintained within the approximatelimits indicated above by suitable additions from time to time. Thefluorides of sodium and potassium are nevertheless relatively stablesubstances in comparison with organic compounds or other substanceswhich are added to molding sands, especially magnesium. molding sand,that decompose or vaporize and escape irom the sand.

Having thus described my invention,

1 claim:

1. The method of controlling the flowability of used molding sandscontaining an argillaceous bonding material which comprises addingthereto, and maintaining therein, from about 0.1'to 2 per cent of atleast one fluoride oi the group consisting of sodium fluoride andpotassium fluoride.

2. The method of controlling the flowability of a used synthetic moldingsand containing from about 2 to 5 per cent bentonite, which comprisesadding thereto and maintaining therein, from about 0.1 to '2 per cent oiat least one fluoride of the group consisting of sodium fluoride andpotassium fluoride.

3. The method of improving the flowability of a used esium molding saidcontaining trom about 2 to 5 per cent bentonite, l to 2 per cent sulfur,and 1 to 2 per cent boric acid, which comprises adding thereto andmaintaining therein, from about 0.1 to 2 per cent of at least onefluoride selected irom the group so cisodi fluoride and-potassiumfluoride.

4. The method of improu 1:; the flowabiiity at a used magnesi rim-1;; dcon i about2to5pereentbentonite,1to2percent sulfur, 1 to 2 per centboric acid, and 1.5 to 2.5 per cent of a polyhydric alcohol, whichcomprises adding thereto and maintaining therein, irom about 0.1 to 2per cent oi at least one fluoride selected from the group consisting 01.sodium fluoride and potassium fluoride.

5. A used molding sand containing an argil-, laceous bonding materialand from about 0.1 to 2 per cent of at least one fluoride selected fromthe group consisting of potassium fluoride and sodium fluoride, saidsand being characterized by a flowability substantially equivalent tothat of the orig inal sand prior 'to use and the addition of saidfluoride constituent.

8. A used molding sand (or casting magnesium containing about 2 to 5 percent bentonite, 1 to 2 per cent sulfur, l to 2 per cent boric acid, and0.1 to 2 per cent of at least one fluoride ircm the group consisting ofpotassium fluoride and sodium fluoride, said sand being characterized bya flowability substantially equivalent to that of the ori inal sandprior to use and the addition of said fluoride constituent.

7. A used molding sand for casting magnesium containing about 2 to 5 percent of an argillaceous bonding material, 1 to 2 per cent sulfur, l to 2per cent boric acid, 0.25 to 0.5per cent pot fluoride, and about 1.5 to2.5 per cent of a polyhydric alcohol, said sand being characterised by aflowability substantially equivalent to that of the original sand priorto use and the addition of said fluoride constituent.

8. A used molding sand for casting magnesium containing about 2 to 5 percent bentonite, 1 to 2 per cent sulfur, 1' to 2 per cent boric acid,0.25 to 0.5 per cent potassium fluoride, and, about 1.5 to 2.5 per centof a nolyhydric alcohoi, said sand being characterized by a flowabilitysubstantially equivalent to that oi. the original d prior to use and theaddition oi said fluoride constituent.

ET T. W630.-

